The use of transdermal drug delivery systems to topically administer an active agent is well known. These systems incorporate the active agent into a carrier composition, such as a polymeric and/or pressure-sensitive adhesive composition, from which the active agent is delivered through the skin or mucosa of the user.
Active-ingredient-containing transdermal drug delivery systems (“patches”) are essentially divided into two major technical systems: reservoir systems and matrix systems. The present invention relates to matrix systems where the active ingredient(s) are embedded in a semi-solid matrix made up of a single polymer or a blend of polymers.
Both types of devices employ a backing layer that forms the protective outer surface of the finished transdermal system and which is exposed to the environment during use. A release liner or protective layer that forms the inner surface covers the polymeric adhesive which is employed for affixing the system to the skin or mucosa of a user. The release liner or protective layer is removed prior to application, exposing the adhesive, typically a pressure-sensitive adhesive.
In the “classic” reservoir-type device, the active agent is typically dissolved or dispersed in a carrier to yield a non-finite carrier form, such as, for example, a fluid or gel. In the reservoir-type device, the active agent is generally kept separate from the adhesive. The device has a pocket or “reservoir” which physically serves to hold the active agent and carrier, and which is formed in or by a backing layer. A peripheral adhesive layer is then used to affix the device to the user.
The reservoir-type devices have a number of disadvantages including a non-uniform drug release profile where a high dose of drug is initially released upon application to the user, often described as a “burst effect.” This burst or high initial release of drug then drops off after a period of time to a rate that necessary to achieve a therapeutically effective amount. Drug delivery according to this profile is generally described as first order release.
While classic reservoir-type devices are still in use today, the term reservoir is being used interchangeably herein with matrix-type devices which still rely upon a separate adhesive means used to affix the device to the user.
In a matrix-type device, the active agent is dissolved or dispersed in a carrier that typically is in a finite carrier form. The carrier form can be self-adhesive or non-adhesive. Non-adhesive matrix-type devices, that is, those which still rely on a separate adhesive means to affix the device to the user, employ a drug permeable adhesive layer (often referred to as an “in-line adhesive” since the drug must pass through this layer) applied over the drug matrix carrier layer. To better control the release rate of the drug, the non-adhesive matrix-type devices often employ one or more additional drug permeable layers such as, for example, rate controlling membranes. The non-adhesive matrix-type devices often contain excipients, such as drug delivery enhancers, to help control the release rate. These devices are often referred to as multilayer or multilaminate.
In a “monolithic” or “monolayer” matrix-type device, the active agent is typically solubilized or homogenously blended in an adhesive carrier composition, typically a pressure-sensitive adhesive or bioadhesive, which functions as both the drug carrier and the means of affixing the system to the skin or mucosa. Such devices, commonly referred to as drug-in-adhesive devices, are described, for example, in U.S. Pat. Nos. 4,994,267; 5,446,070; 5,474,783 and 5,656,286, all of which are assigned to Noven Pharmaceuticals, Inc., Miami, Fla. and herein incorporated by reference.
While matrix-type devices, especially drug-in-adhesive devices, achieve more uniform and controlled drug deliver rates over longer periods of time, most transdermal systems remain subject to a higher initial drug release than is required to achieve therapeutic efficacy. For many drugs and/or therapeutic situations, it would be advantageous to eliminate or suppress this higher initial release and achieve a “steady state” (zero order) release profile which uniformly delivers a therapeutically effective amount of drug over the extended duration of device's desired use, preferably up to 7 days or more.
The high initial blood level concentration of certain drugs may cause adverse or undesired effects, or create toxicity concerns, thereby limiting the use of transdermal administration. In other instances, the higher initial blood level concentration may reduce the amount of drug required for treatment to the point of risking under dosing, or the higher initial blood level concentration may make it impractical to increase the duration of the device's application while retaining therapeutic effectiveness. Reducing the frequency of replacing the transdermal drug delivery system would increase user compliance, reduce any lag or drop off in efficacious blood levels, and reduce the amount of drug required for treatment (also provided by reducing the higher initial blood level associated with the higher release rate).
Drug concentration in transdermal delivery systems can vary widely depending on the drug and polymers used. Low drug concentrations in the adhesive can result in difficulties in achieving an acceptable delivery rate of the medicament, preferably one approximating zero order kinetics. High drug concentrations, on the other hand, frequently affect the adhesion properties of the adhesives, and tend to promote unwanted crystallization and “burst effect” (i.e., rapid drug release).
Simple diffusion models for permeation of drugs through the skin suggest that permeation rates are concentration dependent, that is, dependent on both the amount and the degree of drug within the pressure-sensitive adhesive composition. Some adhesives, such as, for example, polyacrylate adhesives have a high affinity for many drugs and thus tend to solubilize higher concentrations of drug than do, for example, rubber adhesives. However, the use of polyacylates alone as the adhesive is not without its drawbacks as polyacrylate adhesives, for example, may tend to cause skin irritation, especially when the transdermal device is used for extended periods of time.
Various transdermal drug delivery systems have been described in the literature. For example, U.S. Pat. No. 4,559,222 describes a multi-layer non-adhesive matrix-type device having a reservoir layer which comprises mineral oil, colloidal silicon dioxide, a polyisobutylene adhesive and a drug, which may be clonidine, at a concentration greater than saturation. The system includes a drug release rate controlling layer through which the drug may diffuse at a known rate, an adhesive layer, which may also contain a loading of drug, and a protective strippable coating.
U.S. Pat. No. 5,762,952 describes a system comprising a self-crosslinking acrylate adhesive into which a drug, such as clonidine, is incorporated together with auxiliaries, such as solvents or absorption promoters, that are volatile at relatively high temperatures. The patent discusses that the crosslinked acrylate adhesive is important to increase the consistency of the adhesive substance and to incorporate either a large amount of the active drug or a large amount of an inactive solubilizing agent into the adhesive.
Therefore, despite the existence of many different types of transdermal delivery systems in the art, there remains a continuing need for improving the release profile of drugs to achieve substantially zero order, as well as extending the duration of use of each individual transdermal drug delivery system.